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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5052) Option to debug generated Java code using an IDE
Date Fri, 09 Dec 2016 04:36:59 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5052?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15734264#comment-15734264
] 

ASF GitHub Bot commented on DRILL-5052:
---------------------------------------

Github user paul-rogers commented on a diff in the pull request:

    https://github.com/apache/drill/pull/660#discussion_r91631857
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/compile/CachedClassLoader.java
---
    @@ -0,0 +1,70 @@
    +/**
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * or more contributor license agreements.  See the NOTICE file
    + * distributed with this work for additional information
    + * regarding copyright ownership.  The ASF licenses this file
    + * to you under the Apache License, Version 2.0 (the
    + * "License"); you may not use this file except in compliance
    + * with the License.  You may obtain a copy of the License at
    + *
    + * http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +package org.apache.drill.exec.compile;
    +
    +import java.net.URL;
    +import java.net.URLClassLoader;
    +import java.util.Map;
    +import java.util.concurrent.ConcurrentMap;
    +
    +import com.google.common.collect.MapMaker;
    +
    +/**
    + * Class loader for "plain-old Java" generated classes.
    + * Very basic implementation: allows defining a class from
    + * byte codes and finding the loaded classes. Delegates
    + * all other class requests to the thread context class
    + * loader. This structure ensures that a generated class can
    + * find both its own inner classes as well as all the standard
    + * Drill implementation classes.
    + */
    +
    +public class CachedClassLoader extends URLClassLoader {
    +
    +  /**
    +   * Cache of generated classes. Semantics: a single thread defines
    +   * the classes, many threads may access the classes.
    +   */
    +
    +  private ConcurrentMap<String, Class<?>> cache = new MapMaker().concurrencyLevel(4).makeMap();
    --- End diff --
    
    Done.


> Option to debug generated Java code using an IDE
> ------------------------------------------------
>
>                 Key: DRILL-5052
>                 URL: https://issues.apache.org/jira/browse/DRILL-5052
>             Project: Apache Drill
>          Issue Type: Improvement
>          Components: Execution - Codegen
>    Affects Versions: 1.8.0
>            Reporter: Paul Rogers
>            Assignee: Paul Rogers
>            Priority: Minor
>
> Drill makes extensive use of Java code generation to implement its operators. Drill uses
sophisticated techniques to blend generated code with pre-compiled template code. An unfortunate
side-effect of this behavior is that it is very difficult to visualize and debug the generated
code.
> As it turns out, Drill's code-merge facility is, in essence, a do-it-yourself version
of subclassing. The Drill "template" is the parent class, the generated code is the subclass.
But, rather than using plain-old subclassing, Drill combines the code from the two classes
into a single "artificial" packet of byte codes for which no source exists.
> Modify the code generation path to optionally allow "plain-old Java" compilation: the
generated code is a subclass of the template. Compile the generated code as a plain-old Java
class with no byte-code fix-up. Write the code to a known location that the IDE can search
when looking for source files.
> With this change, developers can turn on the above feature, set a breakpoint in a template,
then step directly into the generated Java code called from the template.
> This feature should be an option, enabled by developers when needed. The existing byte-code
technique should be used for production code generation.



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